A direct-drive five-bar manipulator with tuned directional first-order kinematics for low energy consumption in vertical loading

The kinematic configuration space of a manipulator determines the set of all possible motions that may occur, and its differential properties have a strong, albeit indirect, influence on both static and dynamic performance. By viewing first-order kinematics as a field of Jacobian-defined ellipses across a workspace, a novel two degree-of-freedom manipulator was designed, and is tested in this paper for its benefits. The manipulator exhibits a field of ellipses that biases transmission characteristics in Cartesian directions of the end-effector. The horizontal direction is biased toward speed in order to move across the width of the workspace quickly, while the vertical direction is biased toward force production in order to resist gravitational loads. The latter bias endows the manipulator with load capacity in the absence of gears. Such an exclusion can forego the extra weight, complexity, backlash, transmission losses, and fragility of gearboxes. Additionally, a direct drive set-up improves backdrivability and transparency. The latter is relevant to applications that involve interacting with the environment or people. Our novel design is set through an array of theoretical and experimental performance studies in comparison to a conventional direct drive manipulator. The experimental results showed a 3.75× increase in payload capacity, a 2× increase in dynamic tracking accuracy, a 2.07× increase in dynamic cycling frequency, and at least a 3.70× reduction in power consumption, considering both static and dynamic experiments.